Roofing products such as asphalt or bitumen impregnated roof coverings and vapour barriers and the like are today difficult to identify upon the product being dispatched from its place of manufacture.
Manufacturers of such roofing materials have a strong desire in obtaining a simple and cost effective method of applying a unique, reliable and durable identification to their products. Further, manufacturers of the above roof products strive in producing a product comprising an identification system being able to encompass close to an infinite number of identities in order to provide the product with a unique ID being able to hold a precise date, time and location of manufacture.
There are various reasons for such desire, some of which are:                possibility for determining whether a product is actually manufactured by a particular manufacturer in order to prevent and unveil imitations,        possibility for optimization of internal logistic and handling,        possibility for identifying stolen products, and        possibility for tracing the product back to an exact place and time of manufacture.        
Up to this day, roofing products like roll roofing and roofing shingles comprising a bitumen impregnated core provided with at least one further layer of bitumen are either not marked with identification or marked with a simple physical identification “stamp” between the layers or directly on one of its surfaces. Such marking typically consist of a combination of characters constituting an ID of the product.
The marking is typically performed by means of an impression, e.g. from a stamp or a roll arranged in connection with a production line, where the stamp or roll comprises a set of characters which is impressed into the roofing product.
Another common way of identifying a product is by means of an inked stamp applied on the product or on the outer surface of the finished roll of roofing product.
The above techniques hold several drawbacks, some of which are:                difficulties in providing fast changing identifications as the means for impressing into the roofing product typically constitutes fixed characters which are not easily changeable,        difficulties in locating the impressions on the final product,        poor quality of the impressions as the material of the roofing product tends to stick to the means for impression,        poor durability due the nature of the asphalt or bitumen based material, as the material, even after application to a roofing structure, holds a degree of indulgence, the impressions over time is smoothed out, and        imitations of the product incl. identification may be produced relatively easy, as a somewhat exact copy of a stamp is easy obtainable.        
Summative, manufacturers of roofing products wherein the products constitutes layered products like vapour barriers and roof coverings, strive in obtaining a feasible method of manufacturing aforementioned products.
One example of a layered vapour barrier is disclosed in the U.S. Pat. No. 4,567,080 A, which teach a vapour barrier comprising two vapour-tight layers and a water absorbing layer interposed there between.
One example of a layered roof covering is disclosed in GB 2094226 A, which teach a sealing sheet with an upper layer, a strengthening layer and an underside layer. The sheet is used for covering parts of buildings and roofs.
The art includes a number of methods of identifying roofing products, one example is GB 179130 A which suggests identifying the time and place of origin of roofing product by means of a thread embedded within or in between layers constituting the product. The colour of the thread is linked to a particular place of manufacture, whereby the origin of the product may be determined.
The possible variants of the above identification technique is limited to the number of colours available for the thread, and further, information like production date and exact time of production are not immediately applicable.
Today there are more advanced methods of identification available. One of particular interest to manufacturers of roof coverings is the radio frequency identification technique, generally called RFID and described e.g. in U.S. Pat. No. 4,384,288A.
The RFID technique relies on remotely storing and retrieving data using devices called RFID tags or RFID transponders.
An RFID tag is an object that can be applied to or incorporated into a product for the purpose of identification by means of radio waves. Some tags can communicate over several meters and beyond the line of sight of the reading and/or writing instrument.
RFID tags contain at least two parts. The first part is an integrated circuit for storing and processing information, modulating and demodulating a signal and other specialized functions, and the second part is an antenna for receiving and transmitting the signal.
The parts are typically arranged on a base e.g. constituting a piece of foil or a plastic sheet. The tags are in some embodiments sealed by means of a layer of protective foil applied to the surface opposite the base.
RFID tags come in three general varieties: passive, active, or semi-passive.
Passive tags require no internal power source, thus being pure passive devices (they are only active when a reader is nearby to power them via radio waves), whereas semi-passive and active tags require a power source, usually a small battery.
As the passive RFID tags have no internal power supply, the minute electrical current induced in the antenna by the incoming radio frequency signal, is used as power for the electronic circuits in the tag.
A drawback of many of the present RFID tags is that they need an external antenna which is about 80 times larger than the integrated circuit served by the antenna.
As RFID tags today are produced in substantial numbers, the tag by tag cost is typically very low in comparison with the product to which they are applied.
RFID tags may be obtained from various suppliers and in virtually any form, e.g. as a thin “endless” strip from where the tags may be cut one by one.
Another popular way of obtaining a plurality of tags is as thin stickers adhered to a carrying strip. In such embodiments, one surface of the tags is provided with a suitable adhesive.
The RFID tags allows read and write of data which at convenience may constitute place, date and time of production, serial number, manufacturer name and product number etc. The RFID tags even allow for multi-bit encryption and password protection of the data written to the chip.
Manufacturers of roofing products such as vapour barriers and asphalt or bitumen based roofing products, e.g. in the form of roll roofing or roofing shingles, has been seeking methods of manufacture wherein the products are provided with RFID tags, and until now, no feasible method of large scale production has been found.
As the RFID tag, in order to be substantially invisible, and the overall appearance and functionality of final product incl. RFID tag must be equivalent to the overall appearance product without the RFID tag, the tag has to be arranged within the roofing product. As a result of this, the RFID tag must be applied during the manufacturing process, and preferably in between layers constituting the product.
Research and attempts in setting up manufacturing processes of roofing products wherein RFID tags are applied have led to various defects within either the RFID tag or the final product as such. Some of the experienced deficiencies are:                de-lamination of the roofing product in the area of the RFID tag due to the tag changing form from flat to curved as a result of the tag being subjected to the relatively hot manufacturing process,        damage to the RFID tag as a result of the tag being exposed to the harsh environment within the manufacturing process.        
The first object of the present invention is to therefore set forth a method of manufacture in accordance with the introductory part of this specification and wherein the above problems are overcome.
The second object of the present invention is to provide a process plant adapted to manufacturing a roofing product according to the first aspect of the present invention.
The third object of the present invention is to provide a method of identifying a roof where the roofing product is manufactured according the first aspect of the present invention.
The fourth object is the present invention is to provide an identifiable roofing product consisting of a first layer of material, a second layer of material wherein at least one device adapted to communicate via radio waves is arranged in between the first layer of material and the second layer of material.